EN ISO 6946: UK, Ireland, Germany, France, US, Canada & Australia
Build up wall, roof, and floor constructions layer by layer and get U-values, R-values, and condensation risk, checked against primary building regulations across 11 territories. Learn more.
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Design conditions Wall · 20°C / -4°C
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Defaults update to a typical winter design condition for whichever territory (and zone, where applicable) is selected above. These are reasonable starting points based on established climate patterns, not primary-sourced regulatory figures the way the U-value benchmarks are, and always editable. For a real project, source Te/RH from CIBSE Guide A, ASHRAE, or the relevant regional design data for your territory. Rsi (internal surface resistance) follows BS EN ISO 6946:2017 Table 1 by direction of heat flow: 0.13 m²K/W horizontal (wall), 0.10 m²K/W upward (roof), 0.17 m²K/W downward (floor). Rse (external surface resistance) is 0.04 m²K/W throughout, for surfaces exposed to outside air or an unheated void.
The suspended/intermediate floor option covers a floor exposed to an unheated space (e.g. over a ventilated underfloor void, garage, or unheated room) using the simple resistance method above. The ground-bearing floor option instead uses BS EN ISO 13370:2017's ground-coupled method: the ground itself acts as a heat store, so it needs the floor's actual area and exposed perimeter rather than just Rsi+ΣR+Rse. Condensation risk (Glaser) isn't calculated for ground-bearing floors, since the standard doesn't define an equivalent simple vapour-pressure profile against the ground the way it does against outside air.
Framing geometry 38mm @ 600mm centres
Applies to any layer(s) marked Bridged below, including a service void formed with battens. Fraction bridged defaults to width ÷ centres, but you can type a value directly (e.g. to model a known thermal bridging factor from a manufacturer's assessment), or pick one of the BR 443 defaults above to fill it in automatically. All bridged layers are assumed to share the same framing line.
BR 443 is a UK standard (BRE's Conventions for U-value calculations), offered here as a reference point for any territory, since typical timber stud spacing is often similar internationally, but the specific clause numbers and percentages below are UK conventions, not requirements outside the UK. Figures match BR 443's 2006 edition, cited by clause number. The 15%/12.5% standard/enhanced figures are unchanged in the current 2019 edition. The I-beam percentages here follow BR 443's own 2006 text; an industry source (STA Advice Note 19) gives different figures for the same sizes, and it's not established whether that reflects a 2019 update or separate guidance. "Standard" assumes construction conforming with Accredited Construction Details (UK); "enhanced" applies only where the additional detailing conditions in §4.5.1(ii) are also met. Both masonry mortar joint figures apply only when the masonry unit itself is not dense. BR 443 states mortar joints can be disregarded entirely where the unit's thermal conductivity exceeds 0.5 W/mK (roughly, density above 1500 kg/m³), which is the case for most standard dense brick and blockwork; the brick figure (17.2%) is calculated from BR 443's own general formula for "other cases," not a figure the document states directly. Always check against the specific construction and, where relevant, a manufacturer's or designer's calculation.
Regulatory pathway England · New dwelling
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NT's Part 13.2 is structurally different from the rest of Australia: a flat Total R-Value target (2.70) for the roof, varying by roof covering type and zone, rather than the SA/overhang/wall-type matrix used elsewhere. Wall requirements are built around a mass-wall shading exemption (dense walls ≥220kg/m² need shading, not an insulation R-value target) rather than a simple R-value. Since there's no clean confirmed R-value path for wall or floor here, both are shown for reference only, not checked against a target.
Compared as insulation-R against insulation-R (summing only the layers grouped as "Insulation" in your build-up) against the NCC's own table, not a whole-assembly conversion. Some wall construction types genuinely don't have a separate NCC table in every zone (e.g. masonry cavity isn't separately tabulated in Zone 1's tropical climate). That's a real structural feature of the code, not a gap in this tool's data, and is flagged clearly when it applies.
Build-up: internal face → external face
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Your custom materials
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Materials you've named and calculated stay in every material dropdown for the rest of this session, so you can reuse them on other layers without redefining them. On the full plan, use "Save to my library" on any material to keep it permanently, available in every future session, on any device you log into. Delete one here if it was a typo or you no longer need it. Any layer currently using it reverts to a blank Custom layer (its thickness/λ/μ values are kept, but the name is cleared so it doesn't just get re-added on the next calculation) rather than disappearing entirely.
U-Value
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W/m²K
Method
BS EN ISO 6946:2017
Status—
Assembly assessment
Rule-based prompts from this tool's own checks (regulatory benchmark, condensation risk, vapour permeability gradient, thermal bridging fraction, dynamic thermal response): a starting point for review, not a certified assessment.
3D build-up
drag empty space to rotate · scroll or pinch to zoom · click a layer to highlight it · drag a layer to reorder it · set the angle/zoom you want before downloading the PDF
Materials list
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Air cavityStuds/battens drawn as solid blocks through bridged layers · schematic spacing, not to scale
Results
U-value
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W/m²K · BS EN ISO 6946:2017
Total R
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m²K/W incl. surfaces
Total Sd
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m equiv. air layer (unbridged path)
Total thickness
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mm
Weight
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kg/m² · framing-blended, enabled layers
Heat storage capacity
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kJ/m²K · whole assembly
Decrement factor
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amplitude reduction, 24h cycle
Time lag
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hours, decrement delay
Embodied carbon (A1–A3)
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kg CO₂e/m² · cradle-to-gate, user-entered figures only
How this figure works
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This tool has no built-in embodied carbon database. Every material defaults to 0 kg CO₂e/kg. A 0 here means no figure has been entered yet, not that the material is zero-carbon. Enter a project-specific A1–A3 figure per material, plus that same EPD's stated density (kg/m³, density field's neighbour, above); this tool multiplies the two together with each layer's own thickness to build the total, which updates automatically as you do. Most EPDs state A1–A3 per m³, not per kg. Enter that figure directly into the small "or per m³" field beneath CO₂e and it converts for you, or do the division yourself if you already have a per-kg figure.
⚠One or more layers has only a CO₂e or only a density figure set, not both. That layer is silently contributing nothing to the total above until both are entered.
Estimated material cost
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£/m² · supply cost only, user-entered figures
How this figure works
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This tool has no built-in pricing database. Every material defaults to £0/m², meaning no price has been entered yet, not that the material is free. Enter your own supplier quote or list price per material, per m² of wall/roof/floor area (not per m² of the material sheet itself); this tool sums it across every enabled, non-airspace layer to build the per-m² total above. Add a total area to convert that rate into a project total. This is materials supply cost only. It doesn't include labour, waste allowance, delivery, or VAT unless you've built those into the figures you enter, and prices move, so treat this as a rough estimate to sanity-check a quote against, not a substitute for one.
Run this before downloading your PDF report if you want these results included. The download only shows this table if it's been run for the build-up currently on screen; it's cleared whenever you change anything, so it can't accidentally show results for a different build-up. Runs this tool's own temperature/vapour-pressure calculation once per calendar month over a full year (BS EN ISO 13788's monthly method, a fuller check than the single winter design point above) and tracks whether moisture that condenses in the colder months can fully evaporate again before the following winter. Covers all 11 territories, using this tool's own representative seasonal climate data (see the note below the results). England, Scotland, Wales, Northern Ireland and Ireland share the highest-confidence dataset, built from a real professional condensation-risk report; every other territory uses a lower-confidence composite, flagged after each run.
Time lag & decrement factor
The decrement factor and time lag above describe how a 24-hour external temperature cycle is damped and delayed passing through this build-up (between-framing path, same simplification as the Glaser check), calculated using the periodic admittance method behind BS EN ISO 13786:2017 (method implemented, standard's text not reproduced). A low decrement factor and long time lag mean more thermal buffering against summer overheating; a decrement factor near 1 and a short time lag mean the internal face tracks external swings closely. This is a fabric-only indicator, The internal surface curve above is drawn on its own scale, sized to its own real amplitude rather than a fixed daily swing. A well-buffered build-up's actual internal swing can be very small, and this keeps its shape and timing visible rather than flattening it out. The faded external curve is shown for timing reference only (not to a real temperature scale) using an illustrative peak time of 3pm, not a real climate prediction.
Temperature profile: between-framing path (width ∝ R)
Temperature °C
Vapour pressure profile: between-framing path
Actual vapour pressureSaturation vapour pressureCondensation risk (actual > saturation)
U-value with bridged layers uses the ISO 6946 combined method: upper resistance limit (parallel path, between-framing vs through-framing) and lower resistance limit (isothermal planes), averaged. If the two limits diverge by more than ~1.5×, the standard flags the result as indicative only. Service/installation void and reflective cavity layers calculate their R value from thickness, heat-flow direction (from "Building element" above) and surface emissivity (BS EN ISO 6946:2017 Annex D) rather than λ; untick "Calculate" on the layer to enter your own value instead. A rainscreen build-up (timber cladding over a well-ventilated cavity) should use the "Ventilated cavity" preset for the cavity layer. Per BS EN ISO 6946:2017, that layer and anything further outward (the cladding itself) is automatically excluded from the U-value, R and Glaser calculation, since a well-ventilated void is treated as open to outside air; it still appears in the build-up table and 3D view for documentation. The Glaser diagrams and 3D section both use the between-framing path/schematic framing as illustration, not a certified thermal bridging model. λ/μ/R values shown are indicative defaults. Verify against manufacturers' declared values before using for regulatory compliance or building-warranty purposes.
On sources: BS EN ISO 6946:2017, BS 5250:2021 (Management of moisture in buildings — Code of practice, incorporating Corrigendum No. 1; supersedes BS 5250:2011+A1:2016), BS EN ISO 13786:2017 and BS EN ISO 13788:2012 are BSI copyright. This tool implements their calculation methods and cites them by number, but doesn't reproduce their text or published tables.
